Efficient separation of palladium from high-level liquid waste with novel adsorbents prepared by sulfhydryl organic ligands containing imidazole, thiazole and oxazole composited with XAD7HP

Abstract

Separation of palladium from high level liquid waste (HLLW) not only manages the dispose of HLLW, but could also aid in overcoming the shortage of palladium resources. Herein, three novel adsorbents, namely, 2-mercaptobenzimidazole (MBI)/XAD7HP, 2-mercaptobenzothiazole (MBT)/XAD7HP, 2-mercaptobenzoxazole (MBO)/XAD7HP were prepared by vacuum impregnation method using Amberlite XAD7HP resin (XAD7HP) as the carrier for the selective separation of Pd(II) from simulated HLLW. SEM-EDS (Scanning Electron Microscopy), BET (Brunauer-Emmett-Teller) and PXRD (Powder X-ray diffraction) analysis showed that the ligands were successfully impregnated into the carrier. The saturated adsorption capacities of MBI/XAD7HP, MBT/XAD7HP, MBO/XAD7HP in 0.5 M HNO3 were 126.2 mg Pd/g, 137.6 mg Pd/g, 98.4 mg Pd/g, respectively, and excellent adsorption and separation performance towards Pd(II) (SFPd/other metals > 500 and Kd > 104 mL/g from 0.1 to 4 M HNO3) were also achieved. The adsorption kinetics and adsorption isotherms for Pd(II) matched well with pseudo-second-order kinetic model and Langmuir model, indicating that the adsorption for Pd(II) by three adsorbents were monolayer chemical adsorption. The adsorption mechanism was analyzed by FT-IR, XPS combined with DFT calculation. The extremely high selectivity of three adsorbents towards Pd(II) among 15 metal ions is due to the soft N and S donor atoms at ligands which have good affinity for Pd(II) in HNO3 solution. As MBT/XAD7HP exhibited the best adsorption and separation properties, it is supposed to have more application potential for the separation of Pd(II) from HLLW.